Exit pupil expander
An exit pupil expander (EPE) has entrance and exit pupils, a back surface adjacent to the entrance pupil, and an opposed front surface. In one embodiment the EPE is geometrically configured such that light defining a center wavelength that enters at the entrance pupil perpendicular to the back surface experiences angularly varying total internal reflection between the front and back surfaces such that the light exiting the optical channel perpendicular to the exit pupil is at a wavelength shifted from the center wavelength. In another embodiment a first distance at the entrance pupil between the front and back surfaces is different from a second distance at the exit pupil between the front and back surfaces. The EPE may be deployed in a head-wearable imaging device (e.g., virtual or augmented reality) where the entrance pupil in-couples light from a micro display and the exit pupil out-couples light from the EPE.
1. An optical channel comprising:
an optical channel body;
an entrance pupil enabling light to enter the optical channel body;
an exit pupil enabling the light to exit the optical channel body;
a back surface adjacent to the entrance pupil;
a front surface opposite the back surface, wherein the optical channel body is geometrically configured such that the front surface and the back surface are non-parallel; wherein the optical channel body is geometrically configured such that the light defining a center wavelength that enters the optical channel body at the entrance pupil perpendicular to the back surface experiences angularly varying total internal reflection between the front and back surfaces such that the light that exits the optical channel body perpendicular to the exit pupil is at a wavelength shifted from the center wavelength;
and
a wedge overlay, wherein:
the said front and back surfaces are front and back surfaces of the optical channel body;
the wedge overlay defines non-parallel front and back overlay surfaces;
the wedge overlay is disposed adjacent to the front surface of the optical channel body opposite the entrance pupil; and
at least some of the angularly varying total internal reflection between the front and back surfaces are between the front surface of the wedge overlay and the back surface of the optical channel body.
2. The optical channel according to claim 1 , wherein the center wavelength of the light is expanded by the angularly varying total internal reflection such that:
a first portion of the expanded light that exits the optical channel body perpendicular to the exit pupil is at a wavelength shifted from the center wavelength; and
a second portion of the expanded light that exits the optical channel body non-perpendicular to the exit pupil is at the center wavelength.
3. The optical channel according to claim 2 , wherein:
the second portion of the expanded light that exits the optical channel body non-perpendicular to the exit pupil exhibits a greater intensity than the first portion of the expanded light that exits the optical channel body perpendicular to the exit pupil.
4. The optical channel according to claim 1 , wherein the front surface is adjacent to the exit pupil and the optical channel body is a see-through exit pupil expander further comprising:
a compensating wedge disposed adjacent to a portion of the back surface opposite the exit pupil, said compensating wedge transparent to incident environmental light and geometrically configured to offset angular variance the optical channel body imposes on incident environmental light that passes into the optical channel body via the compensating wedge.
5. The optical channel according to claim 4 , wherein the front and back surfaces define at least first and second discrete geometric segments of the optical channel body, wherein the front and back surfaces are parallel in the first discrete geometric segment and non-parallel in at least the second discrete geometric segment.
6. The optical channel according to claim 1 , wherein:
the front and back surfaces of the optical channel body are parallel; and
disposition of a distal end of the wedge overlay relative to the entrance pupil filters incident light passing through the entrance pupil such that only wavelengths above or below a threshold experience the angularly varying total internal reflection while remaining wavelengths experience total internal reflection that is not angularly varying.
7. An optical channel comprising:
an optical channel body;
an entrance pupil enabling light to enter the optical channel body;
an exit pupil enabling the light to exit the optical channel body;
a back surface adjacent to the entrance pupil;
a front surface opposite the back surface;
wherein the optical channel body is configured such that a first distance at the entrance pupil between the front surface and the back surface is different from a second distance at the exit pupil between the front surface and the back surface
and
a wedge overlay, wherein:
the front and back surfaces are front and back surfaces of the optical channel body;
the wedge overlay defines non-parallel front and back overlay surfaces;
the wedge overlay is disposed adjacent to the front surface of the optical channel body opposite the entrance pupil such that the first distance is between the back surface of the optical channel body and the front overlay surface; and
at least some of the light entering the optical channel body via the entrance pupil is reflected from the front overlay surface back into the optical channel body towards the back surface of the optical channel body.
8. The optical channel according to claim 7 , wherein the front and back surfaces of the optical channel are configured to form a continuous wedge defining an angle α that quantifies an amount of non-parallelism between them.
9. The optical channel according to claim 8 , wherein the first distance is greater than the second distance.
10. The optical channel according to claim 7 , wherein the front surface is adjacent to the exit pupil and the optical channel body is a see-through exit pupil expander further comprising:
a compensating wedge disposed adjacent to a portion of the back surface opposite the exit pupil, said compensating wedge transparent to incident environmental light and geometrically configured to offset exit pupil expansion that the optical channel body imposes on incident environmental light that passes into the optical channel body via the compensating wedge.
11. The optical channel according to claim 7 , wherein the front and back surfaces define at least first and second discrete geometric segments of the optical channel body, wherein the front and back surfaces are parallel in the first discrete geometric segment and non-parallel in at least the second discrete geometric segment.
12. The optical channel according to claim 7 , wherein:
the front and back surfaces of the optical channel body are parallel; and
disposition of a distal end of the wedge overlay relative to the entrance pupil filters incident light passing through the entrance pupil such that only wavelengths above or below a threshold are reflected from the front overlay surface into the optical channel body while remaining wavelengths reflected from the front overlay surface are not.
13. A head-wearable imaging device comprising a micro display and an exit pupil expander, wherein the exit pupil expander comprises:
an optical channel body;
an entrance pupil configured to in-couple light from the micro-display;
an exit pupil configured to out-couple light from the exit pupil expander;
a back surface adjacent to the entrance pupil; and
a front surface opposite the back surface, wherein the optical channel body is geometrically configured such that the front surface and the back surface are non-parallel; wherein the exit pupil expander is geometrically configured such that the light defining a center wavelength that enters the optical channel body at the entrance pupil perpendicular to the back surface experiences angularly varying total internal reflection between the front and back surfaces such that the light that exits the optical channel body perpendicular to the exit pupil is at a wavelength shifted from the center wavelength;
and
a wedge overlay, wherein:
the said front and back surfaces are front and back surfaces of the optical channel body;
the wedge overlay defines non-parallel front and back overlay surfaces;
the wedge overlay is disposed adjacent to the front surface of the optical channel body opposite the entrance pupil; and
at least some of the angularly varying total internal reflection between the front and back surfaces are between the front surface of the wedge overlay and the back surface of the optical channel body.
14. The head-wearable imaging device according to claim 13 , wherein the at least portion of the front and back surfaces that are non-parallel are flat.
15. The head-wearable imaging device according to claim 13 , wherein the head-wearable imaging device is a virtual reality imaging device.
16. The head-wearable imaging device according to claim 13 , wherein the head-wearable imaging device is an augmented reality device further comprising a compensating wedge disposed opposite the exit pupil such that incident environmental light that passes into the exit pupil expander through the compensating wedge passes out of the exit pupil expander through the exit pupil without total internal reflection.